Known retarders are frequently of the hydraulic or electromagnetic type and they give rise to problems of size and weight.
Disk brakes are also known that make use of disks made of thermostructural composite material, in particular carbon/carbon (C/C) composite material which provides very good friction behavior and also provides a large saving in weight in comparison with traditional metal disk brakes.
The use of C/C material disk friction devices has already been proposed for transmission brakes or retarders of heavy trucks. Reference can be made in particular to document FR-A-2 607 566 and patent application FR 97 06 959.
The use of such devices as axle brakes on rail vehicles has also been envisaged. Reference can be made in particular to documents FR-A-2 626 541, FR-A-2 697 218, and EP-A-0 478 943.
For heavy road vehicles or for rail vehicles, it would be advantageous to provide retarders or transmission brakes with disks of thermostructural composite material but without requiring the use of hydraulic energy.
Nevertheless, account must be taken both of the high temperatures reached by thermostructural composite materials, in particular C/C materials, when subjected to friction, and the need for high levels of force when pressing the disks together in order to obtain the desired effectiveness, and even though the space available is often very restricted.